Common Definitions for Pressure and Vacuum Applications



Accuracy - The limit of deviation from the set point of a pressure or vacuum switch. It is usually a percentage of full scale.


Actuation Point - See Set Point


Adjustable Range -The limits between which the set point can be adjusted.


Burst Pressure - Pressure which causes failure of the pressure element, resulting in permanent damage.


Cycle - One complete sequence of values usually above, and below the set point, which occurs during a time period.


Dead-band - The minimum change in pressure required to open or close the contacts of a switch.


Differential Pressure- A measured pressure difference between two pressure sources.


Electrical Switching Element - Opens or closes an electrical circuit due to a movement from the pressure or vacuum sensing element.


Hysteresis - The difference in readings of an instrument when it is approached from two different directions.


Maximum System Pressure - The highest pressure that a switch may safely operate at.


Maximum Working Pressure - The designed safe limit of a pressure element for regular use a specified pressure.


Normally Closed - Current flows through the switch until the contact is broken by a pressure or vacuum change.


Normally Open - No current flows through the switch until contact is made by a pressure or vacuum change.


NEMA 4 - Water tight and dust tight enclosure.


NEMA 4X- Water tight, dust tight, and corrosion resistant enclosure.


Pressure, Absolute - A pressure scale based on PSIA “0” or a perfect vacuum.


Pressure, Ambient - The pressure immediately surrounding a pressure switch.


Pressure, Atmospheric - The pressure caused by the actual weight of the Earth’s atmosphere. At sea level atmospheric pressure equals 14.7 PSI, 30” HG, or 760 Torr.


Pressure, Barometric - Actual atmospheric pressure in a specific location.


Pressure, Burst – The maximum pressure the unit can withstand without causing a release of the application media.


Pressure, Differential - The difference between a reference pressure and a variable pressure.


Pressure, Gauge - Uses atmosphere as a zero reference point so there is no compensation for changes in barometric pressure.


Pressure, Maximum System - Normal system pressure level not including surges and spikes.


Pressure Proof - Pressure in excess of the maximum operating pressure to which the sensor may occasionally be subjected to.


Pressure, Sensing Element - The portion of the pressure switch that moves with a change in system fluid pressure. Wasco, Inc. pressure switches use capsule, diaphragm, and piston sensing elements.


Pressure, Switch - An instrument that converts a pressure change to an electrical function.


Radio Noise - Electromagnetic interference (EMI)


Reset Band - The difference in pressure between the set point, and the reset point.


Reset Point - Point at which the electrical switching element snaps back to its original position prior to initial actuation.


Response Time (Reaction Time)- The amount of time taken between a change in pressure, and a change in the electrical signal.


Repeatability - The ability of the switch to actuate repeatedly at the desired set point within the sensors tolerance.


Set Point - The exact point at where the electrical switching occurs. This is generally expressed in PSI, or inches, of mercury.


Set Point Range- The range from which the switch can be set from the lowest, to the highest point.


Switching Current, Maximum - The maximum load (amperage) the electrical switch will carry.


Temperature, Ambient - The temperature immediately surrounding a pressure switch.


Temperature, Shift - A change in set point due to changes in ambient, or fluid temperatures.


Vacuum- The value pressure of below atmospheric pressure.


Wetted Parts - Components that come in direct contact with the process media.


Working Pressure Range - The pressure range where the sensor can safely operate, and still maintain the set point




For any inquiries, questions or services, please call: 805-739-2747 or fill out the following form:


2245 A. Street

Santa Maria, CA 93455

Tel: 805-739-2747

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